This proposal seeks to define the major genes that determine the strength of the murine response to T. spiralis. Four intestinal protective responses have been recognized in mice: a. Anti adult immunity; b. Rapid explusion; c. Anti preadult; d. Anti fecundity. Three of these, anti adult, anti preadult and rapid explusion vary between strains and crosses of responder and non responder produce responder offspring. Major control over rapid expulsion is exerted by what appears to be single dominant autosomal gene expressed in NFR/N mice. This hypothesis will be examined by progeny testing BC1 offspring and parental crosses and F2 x parental crosses. The gene will be examined for linkage to known loci (cell membrane alloantigenic determinants and biochemical markers and if this is successful the chromosomal position of Rae will be determined. In addition the locus will be transferred to an non responding background to examine its reactivity in isolation from the strong responder NFR/N background. Similar procedures will be used to analyze the anti adult and anti preadult responses of mice.